Insulated ultrafine powder, method for producing same, and high dielectric constant resin composite material

ABSTRACT

Provided are an insulated ultrafine powder obtained by adding liquid metal alkoxide to a methanol-containing organic solvent in which a conductive ultrafine powder comprising a carbon material is dispersed and further adding water thereto and a method for producing the same. Also, provided are an insulated ultrafine powder obtained by adding liquid metal alkoxide to a methanol-containing organic solvent in which a conductive ultrafine powder comprising a carbon material is dispersed, further adding a coupling agent having an alkoxide group and then adding water thereto and a method for producing the same. Further, provided is a high dielectric constant resin composite material obtained by blending the insulated ultrafine powder of the present invention with a resin in a volume ratio (insulated ultrafine powder/resin) falling in a range of 5/95 to 50/50.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional of pending U.S. patentapplication Ser. No. 13/386,201, which is a National Phase ofPCT/JP2010/061708 filed Jul. 9, 2010 and claims the benefit of JapaneseApplication No. 2010-029291 filed Feb. 12, 2010 and Japanese ApplicationNo. 2009-175196 filed Jul. 28, 2009. The disclosures of U.S. patentapplication Ser. No. 13/386,201 and PCT/JP2010/061708 are incorporatedby reference herein their entireties.

TECHNICAL FIELD

The present invention relates to an insulated ultrafine powder, a methodfor producing the same and a high dielectric constant resin compositematerial prepared by using the above insulated ultrafine powder.

BACKGROUND ART

One of causes of data errors in IC (integrated circuit) includes aninfluence of high frequency noise. Known is a method for inhibiting theabove matter in which a capacitor having a large capacity is provided ona wiring board to remove high frequency noise. A capacitor having such alarge capacity is produced by forming a high dielectric constant layeron a wiring board. Further, a size of a built-in antenna and a thicknessof a wave absorber are almost inversely proportional to a square root ofa dielectric constant, and therefore a high dielectric constant materialis useful for a reduction in a size and a reduction in a thickness ofthe above members. In particular, resin materials which are excellent ina processability and a moldability are required to be endowed with theabove characteristic.

A resin composite material in which 65 vol % or more, that is, 80 wt %or more of a strong dielectric substance represented by barium titanateis filled as a high dielectric constant filler is proposed as aconventional technique of a high dielectric constant resin compositematerial (refer to, for example, a patent document 1). On the otherhand, a high dielectric constant composition for coating a conductivepowder with an insulated film by a thermosetting resin is proposed(refer to, for example, a patent document 2). However, the stableperformance is not obtained, and therefore it is not commerciallyproduced. Further, a method for coating a metal powder with metal oxide(refer to, for example, a patent document 3) is proposed in recentyears. However, it has to be filled at a high level as is the case withconventional high dielectric constant fillers, and in addition thereto,a metal powder has usually a higher specific gravity than that of metaloxide, so that a specific gravity of a high dielectric constant resincomposite material is as further large as 3 or more.

Further, proposed as well is a method in which a material prepared bywinding a high polymer around a single layer carbon nanotube to insulateit is used for a rise in a dielectric constant of a resin material(refer to, for example, a patent document 4). In the above method,however, the wound high polymer which corresponds to an insulatedcoating film can reversibly be peeled off, and therefore the problemthat the stable performance is not obtained has been involved therein.

Consequently, the existing situation is that in fact, a method in whicha large amount of the filler described above is added is used.Accordingly, a processability, a moldability and a light weight whichare the intrinsic characteristics of a resin material are damaged inexchange for a rise in a dielectric constant thereof.

In order to solve the above problems, the present inventors havedisclosed previously an insulated ultrafine powder prepared by coating aspecific conductive ultrafine powder with specific metal oxide and ahigh dielectric constant resin composite material prepared by using theabove insulated ultrafine powder (refer to, for example, patentdocuments 5 and 6).

RELATED ART DOCUMENTS Patent Documents

-   Patent document 1: Japanese Patent Application Laid-Open No.    237507/2001-   Patent document 2: Japanese Patent Application Laid-Open No.    115800/1979-   Patent document 3: Japanese Patent Application Laid-Open No.    334612/2002-   Patent document 4: Japanese Patent Application Laid-Open (through    PCT) No. 506530/2004-   Patent document 5: International Patent Publication Pamphlet    WO2006/013947-   Patent document 6: Japanese Patent Application Laid-Open No.    94962/2008

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Metal oxide for forming an insulated coating film of the insulatedultrafine powder described above is obtained by depositing metalhydroxide from metal alkoxide by sol-gel reaction in an organic solventin which a conductive ultrafine powder is dispersed, then subjecting itto dehydrating condensation and further subjecting it to surfacetreatment to provide it with a hydrophobicity.

In the insulated ultrafine powder thus obtained, the coating filmobtained by a sol-gel method is porous, and therefore there has beeninvolved therein the problem that while particularly a high dielectricconstant resin composite material in which an insulated ultrafine powderis filled to a high extent is increased in a dielectric constant, tan δshowing a loss of an electric energy is liable to be increased.

As can be found from the above, an object of the present invention is toprovide an insulated ultrafine powder which can reduce tan δ whilemaintaining a dielectric constant of a high dielectric constant resincomposite material in a high state, a method for producing the same anda high dielectric constant resin composite material prepared by usingthe above insulated ultrafine powder.

Means for Solving the Problems

Intense investigations repeated by the present inventors in order tosolve the problems described above have resulted in finding out aninsulated ultrafine powder which provides a resin composite materialwith a high dielectric constant while inhibiting an increase in tan δ bya simple method, a method for producing the same and a high dielectricconstant resin composite material prepared by using the above insulatedultrafine powder. That is, the present invention shall be shown below.

[1] An insulated ultrafine powder obtained by adding liquid metalalkoxide to a methanol-containing organic solvent in which a conductiveultrafine powder comprising a carbon material is disperse and furtheradding water thereto.

[2] An insulated ultrafine powder obtained by adding liquid metalalkoxide to a methanol-containing organic solvent in which a conductiveultrafine powder comprising a carbon material is dispersed, furtheradding an organic silicon compound or a coupling agent and then addingwater thereto.[3] The insulated ultrafine powder according to the above item [1] or[2], wherein a cross-sectional diameter of the conductive ultrafinepowder comprising a carbon material is 1 nm or more and 500 nm or less.[4] The insulated ultrafine powder according to the above item [1] or[2], wherein the carbon material constituting the conductive ultrafinepowder is a carbon nanofiber, natural graphite, carbon black, a carbonnanotube or artificial graphite.[5] The insulated ultrafine powder according to the above item [1] or[2], wherein a constitutional metal element of the liquid metal alkoxidecontains at least any one kind of Ti and Zr.[6] The insulated ultrafine powder according to the above item [2],wherein the coupling agent is a silane base coupling agent.[7] A high dielectric constant resin composite material obtained byblending the insulated ultrafine powder according to the above item [1]or [2] with a resin in a volume ratio (insulated ultrafine powder/resin)falling in a range of 5/95 to 50/50.[8] The high dielectric constant resin composite material according tothe above item [7], wherein the resin is a thermoplastic resin.[9] The high dielectric constant resin composite material according tothe above item [7], wherein the resin is any of polypropylene,polystyrene, modified polyphenylene ether, polybutylene terephthalateand polyphenylene sulfide.[10] The high dielectric constant resin composite material according tothe above item [7], wherein a specific gravity thereof is 2 or less.[11] The high dielectric constant resin composite material according tothe above item [7], further containing a filler.[12] The high dielectric constant resin composite material according tothe above item [7], wherein a specific inductive capacity thereof is 10or more.[13] A method for producing an insulated ultrafine powder, whereinliquid metal alkoxide is added to a methanol-containing organic solventin which a conductive ultrafine powder comprising a carbon material isdispersed, and water is further added thereto.[14] A method for producing an insulated ultrafine powder, whereinliquid metal alkoxide is added to a methanol-containing organic solventin which a conductive ultrafine powder comprising a carbon material isdispersed; a coupling agent having an alkoxide group is further added;and then water is added thereto.

According to the present invention, capable of being provided aninsulated ultrafine powder which can reduce tan 6 while maintaining adielectric constant of a high dielectric constant resin compositematerial in a high state, a method for producing the same and a highdielectric constant resin composite material prepared by using the aboveinsulated ultrafine powder.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning electron micrograph of an insulated ultrafinepowder obtained by the synthetic method 1 for an insulated ultrafinepowder.

FIG. 2 is a scanning electron micrograph of an insulated ultrafinepowder obtained by the synthetic method 3 for an insulated ultrafinepowder.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

1. Insulated Ultrafine Powder and Method for Producing the Same:

The first insulated ultrafine powder of the present invention isobtained by adding liquid metal alkoxide to a methanol-containingorganic solvent in which a conductive ultrafine powder comprising acarbon material is dispersed and further adding water thereto.

Further, the second insulated ultrafine powder of the present inventionis obtained by adding liquid metal alkoxide to a methanol-containingorganic solvent in which a conductive ultrafine powder comprising acarbon material is dispersed, further adding an organic silicon compoundor a coupling agent and then adding water thereto.

The first insulated ultrafine powder and the second insulated ultrafinepowder according to the present invention (hereinafter, they shall becollectively referred to as “the insulated ultrafine powder of thepresent invention”) shall be explained below in detail.

A powder which reduces a volume resistance of a resin composite materialwhen added alone to the resin material, that is, which has an effect ofproviding an electric conductivity is used as the insulated ultrafinepowder according to the present invention. To be specific, used is aconductive carbon material such as natural graphite, artificialgraphite, furnace carbon black, graphitized carbon black, carbonnanotube, carbon nanofiber and the like.

In contrast with the conductive carbon material, an ultrafine powder ofmetal which is a representative conductive substance is not onlysusceptible to oxidation excluding a part of noble metals and liable tobe reduced in conductivity but also is likely to be subjected to dustexplosion. Also, a metal atom is diffused from the ultrafine powder intoan insulating medium to reduce an insulating property of a resincomposite material. In contrast with this, the conductive carbonmaterial does not bring about the above problems. Further, the carbonmaterial has a small specific gravity of 2.2 and has characteristicswhich are not imparted to other conductive substances and conventionalhigh dielectric constant fillers, and it has as well an effect of areduction in a weight of a high dielectric constant composite material.

The conductive ultrafine powder used in the present invention includesspherical carbon materials having a particle diameter of preferably 1 nmor more and 500 nm or less, more preferably 5 nm or more and 300 nm orless and further preferably 10 nm or more and 100 nm or less. Suchspherical carbon materials, for example, carbon blacks are obtained bythermally cracking hydrocarbon raw materials in a gas phase. Further,graphitized carbon blacks are obtained by vaporizing carbon materials byarc discharge in an atmosphere system of He, CO or a mixed gas thereofin a depressurized vessel maintained at an inner pressure of 2 to 19Torr and cooling and solidifying the vaporized carbon gas.

To be specific, they include SEAST S, TOKABLACK #7100F, conductivecarbon blacks #5500, #4500, #4400 and #4300, graphitized carbon blacks#3855, #3845 and #3800 each manufactured by Tokai Carbon Co., Ltd.,#3050B, #3030B, #3230B, #3350B, MA7, MA8 and MA11 each manufactured byMitsubishi Chemical Corporation and Ketjen Black EC and Ketjen BlackEC600JD each manufactured by Lion Corporation.

In this regard, the term “spherical” does not have to be strictlyspherical and may be an isotropic form. It may be, for example, apolyhedron having edges. Also, when it is not spherical, the “particlediameter” means the smallest diameter.

Also, the conductive ultrafine powder used in the present inventionincludes fibrous carbon materials having a cross-sectional diameter ofpreferably 1 nm or more and 500 nm or less, more preferably 5 nm or moreand 300 nm or less and further preferably 10 nm or more and 200 nm orless. A length thereof is preferably 3 times or more and 300 times orless of the sectional diameter.

The above fibrous carbon materials, for example, carbon nanofibers andcarbon nanotubes are obtained by mixing organic metal compounds ofcobalt and iron which are catalysts with hydrocarbon raw materials in agas phase and heating them. Further, the carbon nanofibers are obtainedby melting and spinning phenol base resins and heating them underinactive atmosphere.

To be specific, they include VGCF and VGNF each manufactured by ShowaDenko K.K., Carbel manufactured by GSI Creos Corporation and carbonnanofibers manufactured by Gun Ei Chemical Industry Co., Ltd.

In this regard, the term “fibrous” means a form extending toward asingle direction and may be, for example, square timber-like, roundbar-like and subspherical. When it is square timber-like, the“cross-sectional diameter” means the smallest diameter.

Further, the conductive ultrafine powder used in the present inventionincludes tabular carbon materials having a thickness of preferably 1 nmor more and 500 nm or less, more preferably 5 nm or more and 300 nm orless and further preferably 10 nm or more and 200 nm or less. A lengthand a width thereof are preferably 3 times or more and 300 times or lessof the sectional diameter.

The above tabular carbon materials are obtained by, for example,refining, crushing and classifying natural graphite and artificialgraphite. They include, for example, SGP series, SNO series and the likeeach manufactured by SEC CARBON LTD. and scale-like-graphite powders,flaked graphite powders and the like each manufactured by NipponGraphite Industries, Ltd. They may be further crushed and preciselyclassified.

In this regard, the term “tabular” means a form in which one directionshrinks and may be, for example, flat sphere-like and flaky.

Controlling a diameter, a cross-sectional diameter or a thickness of theabove particles to the ranges described above makes it possible toprevent the conductivity from being reduced by a quantum size effect.Further, production thereof is facilitated to make it possible toindustrially use them, and a handling property thereof can be made moredifficult to be reduced by aggregation. Further, a continuous layer cansufficiently be formed in a range of 50 vol % or more, that is, a rangeof an addition rate at which the resin characteristics are notdeteriorated.

Further, when a form of the conductive ultrafine powder is fibrous ortabular, an aspect ratio thereof is preferably 3 to 300. The conductiveultrafine powder used in the present invention is more preferablyfibrous than spherical and tabular. This is because an addition amountof the fibrous ultrafine powder which is required for forming acontinuous layer of the resin composite material having a specificinductive capacity of 20 or more can be reduced to, for example, 30 vol% or less.

The particle diameter, the cross-sectional diameter, the thickness andthe aspect ratio can be determined by means of a scanning electronmicroscope.

In the present invention, an insulated coating film is formed on asurface of the conductive ultrafine powder by adding liquid metalalkoxide to the methanol-containing organic solvent in which theconductive ultrafine powder comprising a carbon material is disperse andfurther adding water thereto.

The liquid metal alkoxide used for forming the insulated coating film ismetal alkoxide which stays in a liquid state at a temperature of lowerthan a boiling point of methanol, that is, lower than 64.7° C. at anatmospheric pressure. It includes, for example, tetraethoxytitaniumhaving a melting point of 54° C.

Particularly preferred are alkoxytitanium such astetraisopropoxytitanium, tetra-normal-butoxytitanium, atetra-normal-butoxytitanium dimer, tetra-2-ethylhexoxytitanium,triethoxymonopropoxytitanium and the like; and alkoxyzirconium such astetra-secondary-butoxyzirconium, tetra-tertiary-butoxyzirconium and thelike, which are liquid at room temperature.

A content of methanol in the methanol-containing organic solvent ispreferably 5% by weight or more, more preferably 12% by weight or more,further preferably 20% by weight or more and particularly preferably100% by weight. The organic solvent used together with methanol includeethanol, 2-propanol, acetone, 2-butanone, tetrahydrofuran,dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, hexane,toluene, xylene and the like.

A use amount of the methanol-containing organic solvent is regulated byan amount of methanol in the above methanol-containing organic solventand an amount of the liquid metal alkoxide added. To be specific, anamount of methanol used is preferably an amount in which a methoxy groupis formed by alcohol substitution reaction of the liquid metal alkoxideand in which solid metal methoxide is formed, and it is controlledpreferably to a content of 4 times (mole ratio) or more of the liquidmetal alkoxide.

Further, methanol may be added after adding the liquid metal alkoxide toan organic solvent (for example, an organic solvent other than methanoldescribed above) in which the conductive ultrafine powder comprising acarbon material is disperse to result in preparing themethanol-containing organic solvent. Methanol may be added to theorganic solvent together with or alternately with the liquid metalalkoxide.

In the present invention, methanol as the organic solvent is anessential component, and this is a very important component since aprecursor (for example, tetramethoxytitanium) of an insulated coatingfilm is formed on a surface of the conductive ultrafine powder by makinguse of that the liquid metal alkoxide is turned into a solid material byalcohol substitution reaction. Further, hydrolysis reaction anddehydrating polycondensation reaction proceed by adding water, and aminute TiO₂ insulated coating film is formed on a surface of theconductive ultrafine powder.

A hydroxyl group remains on a surface of the ultrafine powder on whichthe insulated coating film is formed by the method described above. Theabove surface hydroxyl group cross-links the insulated ultrafine powdersby a coating film of insulated metal alkoxide by hydrating condensationfollowed by filtering and drying. That is, it solidifies the insulatedultrafine powder in a certain case. Accordingly, in a case ofcompounding with the resin material in which a strong stress is exertedon the insulated ultrafine powder, breakage of the insulated coatingfilm is liable to be brought about in melting and kneading with athermoplastic resin on a mass production condition using, for example, adouble shaft extruding equipment, and the dielectric characteristic isdestabilized. In order to prevent the above matter, the insulatedultrafine powder is subjected preferably, as is the case with the secondinsulated ultrafine powder of the present invention, to surfacetreatment by an organic silicon compound or a coupling agent(particularly a coupling agent having an alkoxide group) to be turnedinto hydrophobicity.

In order to obtain the second insulated ultrafine powder of the presentinvention, first the liquid metal alkoxide is added, as is the case withthe first insulated ultrafine powder, to the methanol-containing organicsolvent in which the conductive ultrafine powder comprising a carbonmaterial is dispersed. Thereafter, an organic silicon compound or acoupling agent (particularly a coupling agent having an alkoxide group)is further added thereto, and then water is added to thereby obtain thesecond insulated ultrafine powder.

In the reaction for obtaining the second insulated ultrafine powder ofthe present invention, the reaction of the liquid metal alkoxide withthe organic silicon compound or the coupling agent and water can beallowed to proceed at an ordinary temperature and an ordinary pressurein the methanol-containing organic solvent in which the conductiveultrafine powder is dispersed. That is, the steps of adding acid andalkali catalysts for promoting reaction after forming a TiO₂ coatingfilm as ever, dehydrating and distilling become unnecessary, andtherefore the insulated ultrafine powder having a high productivity canbe prepared.

The organic silicon compound used for surface treatment in the presentinvention is at least one compound selected from the group consisting ofalkoxysilanes, organosilane compounds produced from alkoxysilanes,polysiloxanes, modified polysiloxanes, end-modified polysiloxanes andfluoroalkylsilanes. Among them, alkoxysilanes, fluoroalkylsilanes andpolysiloxanes are preferred.

The alkoxysilanes include, to be specific, methyltriethoxysilane,dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane,dimethyldimethoxysilane, methyltrimethoxysilane, phenyltrimethoxysilane,diphenyldimethoxysilane, isobutyltrimethoxysilane,decyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane,γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane,γ-mercaptopropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane,N-β(aminoethyl)-γ-aminopropyltrimethoxysilane,γ-glycidoxypropylmethyldimethoxysilane and the like.

Considering an adhesion strength to insulating metal oxide or metaloxide coating film particles formed on the conductive ultrafine powder,more preferred are alkoxysilanes such as methyltriethoxysilane,methyltrimethoxysilane, dimethyldimethoxysilane,isobutyltrimethoxysilane, phenyltriethoxysilane and the like ororganosilane compounds produced from the above alkoxysilanes.

Also, polysiloxanes having a methylhydrogensiloxane unit,polyether-modified polysiloxanes and end carboxylic acid-modifiedpolysiloxanes in which an end is modified by carboxylic acid can belisted as the polysiloxanes.

The fluoroalkylsilanes include, to be specific,trifluoropropyltrimethoxysilane, tridecafluorooctyltrimethoxysilane,heptadecafluorodecyltrimethoxysilane,heptadecafluorodecylmethyldimethoxysilane, trifluoropropylethoxysilane,tridecafluorooctyltriethoxysilane, heptadecafluorodecyltriethoxysilaneand the like.

Also, at least one compound selected from the group consisting of silanebase, titanate bas, aluminate base and zirconate base silane couplingagents can be used as the coupling agent used for surface treatment.

Among the coupling agents described above, the silane base couplingagents include a part of the organic silane compounds listed above, thatis, alkoxysilanes, and silane base coupling agents other thanalkoxysilanes include methyltrichlorosilane, phenyltrichlorosilane,dimethyldichlorosilane, methyltrichlorosilane, phenyltrichlorosilane,diphenyldichlorosilane, isobutyltrichlorosilane, decyltrichlorosilane,vinyltrichlorosilane, γ-aminopropyltrichlorosilane,γ-glycidoxypropyltrichlorosilane, γ-mercaptopropyltrichlorosilane,γ-methacryloxypropyltrichlorosilane,N-β(aminoethyl)-γ-aminopropyltrichlorosilane and the like.

The titanate base coupling agents include isopropyltristearoyl titanate,isopropyltris(dioctylpyrophosphate) titanate,isopropyltri(N-aminoethyl-aminoethyl) titanate,tetraoctylbis(ditridecylphosphate) titanate,tetra(2-2-diallyloxymethyl-1-butyl)bis(ditridecyl)phosphate titanate,bis(dioctylpyrophosphate)oxyacetate titanate,bis(dioctylpyrophosphate)ethylene titanate and the like.

The aluminate base coupling agents include acetoalkoxyaluminumdiisopropylate, aluminum diisopropoxymonoethylacetoacetate, aluminumtrisethylacetoacetate, aluminum trisacetylacetoacetate and the like.

The zirconate base coupling agents include zirconiumtetrakisacetylacetonate, zirconium dibutoxybisacetylacetonate, zirconiumtetrakisethylacetoacetate, zirconium tributoxymonoethylacetoacetate,zirconium tributoxyacetylacetonate and the like.

A use amount of the surface treating agent is varied according to adegree of the surface hydroxyl group amount, and it is preferably 0.01to 30 parts by weight based on 100 parts by weight of the insulatedultrafine powder (that is, the first insulated ultrafine powder) beforesubjected to the treatment. If it falls in the above range, theinsulated ultrafine powder can sufficiently be dispersed in the resin,and an adhesive property of the insulated ultrafine powder with theresin can be secured as well. It is more preferably 0.1 to 25 parts byweight, particularly preferably 1 to 15 parts by weight.

After the insulated ultrafine powder is filtered and dried passingthrough the surface treatment, it may be further subjected to calciningtreatment. The calcining treatment is preferably carried out bymaintaining the insulated ultrafine powder in a temperature range of 200to 1000° C. for 30 minutes to 24 hours. However, when the conductiveultrafine powder is a carbon material, the calcining atmosphere has tobe non-oxidative. That is, substitution with nitrogen and argon has tobe carried out to cut off oxygen.

2. High Dielectric Constant Resin Composite Material:

The high dielectric constant resin composite material of the presentinvention is obtained by blending the insulated ultrafine powder of thepresent invention with the resin in a volume ratio (insulated ultrafinepowder/resin) of 5/95 to 50/50, that is, the insulated ultrafine powderof the present invention in a range of 5 to 50 vol %.

The high dielectric constant resin composite material having a specificinductive capacity of 20 or more is obtained by blending the insulatedultrafine powder of the present invention in an amount of 50 vol % orless. When a conventional high dielectric constant filler is used, about50 vol % or more of the above filler has to be blended in order toobtain the high dielectric constant resin composite material having aspecific inductive capacity of 20 or more, but when the insulatedultrafine powder of the present invention is used, 5 to 50 vol % of theabove insulated ultrafine powder is suitably blended. Accordingly, theresin composite material prepared by blending the insulated ultrafinepowder of the present invention exerts a high dielectric constantwithout damaging a molding processability and a light weight propertywhich are the intrinsic characteristics of the resin material.

In the present invention, the resin component to which the insulatedultrafine powder described above is added may be either of athermoplastic resin and a thermosetting resin, and a thermoplastic resinis preferred.

The thermoplastic resin includes general purpose plastics such aspolyethylene, polyvinyl chloride, polypropylene, polystyrene, polyvinylacetate, ABS resins, AS resins, acryl resins and the like, engineeringplastics such as polyacetal, polyamide, polycarbonate, modifiedpolyphenylene ether, polybutylene terephthalate and the like and superengineering plastics such as polyallylate, polysulfone, polyphenylenesulfide, polyethersulfone, polyetheretherketone, polyimide resins,fluororesins, polyamideimide and the like. Among them, it is preferablyany of polypropylene, polystyrene, modified polyphenylene ether,polybutylene terephthalate and polyphenylene sulfide.

The thermosetting resin includes phenol resins, amino resins (urearesins, melamine resins, benzoguanamine resins), unsaturated polyesterresins, diallyl phthalate resins (allyl resins), alkyd resins, epoxyresins, urethane resins (polyurethane), silicone resins (silicone) andthe like.

The high dielectric constant resin composite material of the presentinvention can be used by further adding, if necessary, a filler for apurpose other than a high dielectric constant. The filler includes glassfibers for improving the elastic modulus, calcium carbonate for reducingthe molding shrinkage rate, talc used for improving the surface flatnessand the abrasion resistance and mica used for improving the dimensionstability. Further, a filler for providing the flame retardancy, thatis, a flame retardant includes halogen base or phosphorus base flameretardants, aluminum hydroxide and magnesium hydroxide.

When the high dielectric constant resin composite material is used as awave absorber, capable of being further added are ferrite powders usedfor controlling a radio wave absorption characteristic by conventionaltechniques, magnetic metal powders comprising iron as a principalcomponent, conductive powders of a carbon base and a tin oxide base andexfoliated graphite powders which are conductive powders having as wellan effect as a flame retardant.

In the present invention, an addition amount of the insulated ultrafinepowder to the resin composition is, as already described, 5 to 50 vol %,preferably 5 to 30 vol %. If it is smaller than 5 vol %, the continuouslayer is not formed in the resin composition, and the satisfactoryspecific inductive capacity is not obtained. On the other hand, if it islarger than 50 vol %, an intrinsic processability of the resincomposition is damaged.

In the high dielectric constant resin composite material of the presentinvention, the carbon material is used for a raw material of theinsulated ultrafine powder, and therefore a specific gravity thereof canbe reduced to 2 or less.

When the high dielectric constant resin composite material of thepresent invention is used for an antenna substrate, the above highdielectric constant resin composite material has preferably a specificinductive capacity of 20 or more. Wiring patterns are provided at leaston one surface of a layer having a thickness of 1 μm or more and 3 mm orless which is formed from the above high dielectric constant resincomposite material, to be more specific, a film molded therefrom in athickness of 1 μm to 100 μm or a sheet molded therefrom in a thicknessof 100 μm to 3 mm, whereby the antenna substrate can be formed.

Further, a through-hole can be provided as well, if necessary, on thefilm or the sheet of the high dielectric constant resin compositematerial.

When the high dielectric constant resin composite material of thepresent invention is used for a non-contact IC card/tag, IC may be wireddirectly on the wiring patterns of an antenna substrate, or a card/taghaving built-in IC may be brought into contact with the antennasubstrate to use it as a booster antenna. Further, when a film or asheet of the high dielectric constant resin composite material of thepresent invention is used as an antenna substrate and a non-contact ICcard, a protective film may be stuck thereof if necessary.

A wave absorber having a specific inductive capacity of 20 or more isobtained by blending the insulated ultrafine powder of the presentinvention with the resin in an amount of 5 vol % or more and 50 vol % orless. When a conventional high dielectric constant filler is used, about50 vol % or more of the above filler has to be blended in order toobtain the high dielectric constant resin composite material having aspecific inductive capacity of 20 or more, but when the insulatedultrafine powder of the present invention is used, 50 vol % or less, forexample, 5 to 50 vol % of the above insulated ultrafine powder issuitably blended. Accordingly, the resin composite material prepared byblending the insulated ultrafine powder of the present invention exertsa high dielectric constant without damaging a molding processability anda light weight property which are the intrinsic characteristics of theresin material.

A wave absorber prepared by using the above high dielectric constantresin composite material of the present invention has a high dielectricconstant, and therefore when it is turned into a sheet, a thicknessthereof to a wavelength of an electric wave to be absorbed can be set to1/20 or less. A wave absorber prepared by using the above highdielectric constant resin composite material of the present inventioncan be used in an inside of a case and shows an excellent performance asan electronic equipment. Further, the carbon material is used for theraw material of the insulated ultrafine powder, and therefore a specificgravity of the wave absorber can be reduced to 2 or less to make itpossible to reduce further a weight thereof.

EXAMPLE

Next, the present invention shall be explained in further details withreference to examples and comparative examples, but the presentinvention shall by no means be restricted by these examples.

The resin composite material was molded into a disk of 30 mmφ and athickness of 3 mm, and a specific inductive capacity thereof wasmeasured at room temperature and 1 MHz by means of an impedance analyzer(4294A manufactured by Agilent Technologies, Inc.).

Synthesizing Method 1 for Insulated Ultrafine Powder:

A 2 L glass-made reaction vessel was used, and 100 parts by weight ofcarbon black (spherical particles having a diameter of 50 to 100 nm andan average particle diameter of 40 nm) and 100 parts by weight oftetraisopropoxytitanium were added to 800 parts by weight of methanoland stirred and mixed at 30° C. for 1 hour. Next, 10 parts by weight ofphenyltrimethoxysilane was added thereto and mixed for 30 minutes.Further, 30 parts by weight of distilled water was dropwise addedthereto in 30 minutes and stirred for 2 hours to obtain a carbon blackparticles insulated by TiO₂/methanol dispersion liquid. Next, a wet cakeobtained by subjecting the above dispersion liquid to solid-liquidseparation by means of a vacuum filtering bottle was dried by means of avacuum dryer to thereby obtain carbon black particles (insulatedultrafine powder) insulated by TiO₂. The above insulated ultrafinepowder was observed at a magnification of 400,000 times under a scanningtransmission electron microscope (HD-2300 manufactured by HitachiHi-Technologies Corporation) to confirm that a TiO₂ coating film wasformed on a surface of the carbon black. It was found that a coatingfilm state thereof was flat and that the coating film was minute (FIG.1).

Synthesizing Method 2 for Insulated Ultrafine Powder:

Synthesis was carried out in the same manner to obtain carbon blackparticles (insulated ultrafine powder) insulated by TiO₂, except that inthe synthesizing method 1, the solvent was changed to amethanol/2-butanone (100 parts by weight/70 parts by weight) mixedsolvent.

Synthesizing Method 3 for Insulated Ultrafine Powder:

A 2 L glass-made reaction vessel was used, and 100 parts by weight ofcarbon black (spherical particles having a diameter of 50 to 100 nm andan average particle diameter of 40 nm) and 100 parts by weight oftetraisopropoxytitanium were added to 800 parts by weight of isopropanoland stirred and mixed at 30° C. for 1 hour. Next, 10 parts by weight ofphenyltrimethoxysilane was added thereto and mixed for 30 minutes.Further, 30 parts by weight of distilled water was dropwise addedthereto in 30 minutes and stirred for 2 hours to obtain a carbon blackparticles insulated by TiO₂/isopropanol dispersion liquid. Next, a wetcake obtained by subjecting the above dispersion liquid to solid-liquidseparation by means of a vacuum filtering bottle was dried by means of avacuum dryer to thereby obtain carbon black particles (insulatedultrafine powder) insulated by TiO₂. The above insulated ultrafinepowder was observed at a magnification of 400,000 times under thescanning transmission electron microscope (HD-2300 manufactured byHitachi Hi-Technologies Corporation) to confirm that a TiO₂ coating filmwas formed on a surface of the carbon black. It was found that a coatingfilm state thereof was irregular in many portions and that voids werepresent (FIG. 2).

Synthesizing Method 4 for Insulated Ultrafine Powder:

Synthesis was carried out in the same manner to obtain carbon nanofiberparticles (insulated ultrafine powder) insulated by TiO₂, except that inthe synthesizing method 1, carbon nanofiber (fibrous form having across-sectional diameter of 150 nm and a length of 5 to 6 μm) was usedin place of carbon black.

Synthesizing Method 5 for Insulated Ultrafine Powder:

Synthesis was carried out in the same manner to obtain natural graphiteparticles (insulated ultrafine powder) insulated by TiO₂, except that inthe synthesizing method 1, natural graphite (tabular form having athickness of 100 to 200 nm, an average thickness of 150 nm, a square of1 to 3 μm and an average square of 2 μm) was used in place of carbonblack.

Synthesizing Method 6 for Insulated Ultrafine Powder:

Synthesis was carried out in the same manner to obtain carbon blackparticles (insulated ultrafine powder) insulated by ZrO₂, except that inthe synthesizing method 1, tetra-tertiary-butoxyzirconium was used inplace of tetraisopropoxytitanium.

Example 1

The insulated ultrafine powder obtained in the synthesizing method 1 forinsulated ultrafine powder and polyphenylene sulfide (PPS) were moltenand kneaded at 300° C. by means of a melt kneading equipment so that avolume ratio of insulated ultrafine powder/PPS was 25/75, and themixture was pelletized to obtain a resin composite material.

A dielectric constant thereof at 1 MHz was measured to find that aspecific inductive capacity was 25 and that a dielectric loss tangentwas 0.01. Further, a specific gravity of the resin composite materialwas 1.49.

Example 2

The components were molten and kneaded at 300° C. by means of a meltkneading equipment in the same manner as in Example 1, except that avolume ratio of insulated ultrafine powder/PPS was changed to 20/80, andthe mixture was pelletized to obtain a resin composite material.

A dielectric constant thereof at 1 MHz was measured to find that aspecific inductive capacity was 20 and that a dielectric loss tangentwas 0.006. Further, a specific gravity of the resin composite materialwas 1.46.

Example 3

The components were molten and kneaded at 300° C. by means of a meltkneading equipment in the same manner as in Example 1, except that avolume ratio of insulated ultrafine powder/PPS was changed to 30/70, andthe mixture was pelletized to obtain a resin composite material.

A dielectric constant thereof at 1 MHz was measured to find that aspecific inductive capacity was 40 and that a dielectric loss tangentwas 0.02. Further, a specific gravity of the resin composite materialwas 1.52.

Example 4

The components were molten and kneaded at 300° C. by means of a meltkneading equipment in the same manner as in Example 3, except that theparticles synthesized in the synthesizing method 2 for insulatedultrafine powder were used, and the mixture was pelletized to obtain aresin composite material.

A dielectric constant thereof at 1 MHz was measured to find that aspecific inductive capacity was 39 and that a dielectric loss tangentwas 0.02. Further, a specific gravity of the resin composite materialwas 1.52.

Comparative Example 1

The components were molten and kneaded at 300° C. by means of a meltkneading equipment in the same manner as in Example 3, except that theparticles synthesized in the synthesizing method 3 for insulatedultrafine powder were used, and the mixture was pelletized to obtain aresin composite material.

A dielectric constant thereof at 1 MHz was measured to find that aspecific inductive capacity was 39 and that a dielectric loss tangentwas 0.04. Further, a specific gravity of the resin composite materialwas 1.52.

Example 5

The components were molten and kneaded at 300° C. by means of a meltkneading equipment in the same manner as in Example 1, except that theparticles synthesized in the synthesizing method 4 for insulatedultrafine powder were used, and the mixture was pelletized to obtain aresin composite material.

A dielectric constant thereof at 1 MHz was measured to find that aspecific inductive capacity was 28 and that a dielectric loss tangentwas 0.01. Further, a specific gravity of the resin composite materialwas 1.45.

Example 6

The components were molten and kneaded at 300° C. by means of a meltkneading equipment in the same manner as in Example 1, except that theparticles synthesized in the synthesizing method 5 for insulatedultrafine powder were used, and the mixture was pelletized to obtain aresin composite material.

A dielectric constant thereof at 1 MHz was measured to find that aspecific inductive capacity was 25 and that a dielectric loss tangentwas 0.008. Further, a specific gravity of the resin composite materialwas 1.45.

Example 7

The components were molten and kneaded at 300° C. by means of a meltkneading equipment in the same manner as in Example 1, except that theparticles synthesized in the synthesizing method 6 for insulatedultrafine powder were used, and the mixture was pelletized to obtain aresin composite material.

A dielectric constant thereof at 1 MHz was measured to find that aspecific inductive capacity was 26 and that a dielectric loss tangentwas 0.012. Further, a specific gravity of the resin composite materialwas 1.49.

Example 8

The insulated ultrafine powder obtained in the synthesizing method 1 forinsulated ultrafine powder, polyphenylene ether (PPE) and polystyrene(PS) were molten and kneaded at 270° C. by means of a melt kneadingequipment so that a volume ratio of insulated ultrafine powder/PPE/PSwas 25/37.5/37.5, and the mixture was pelletized to obtain a resincomposite material.

A dielectric constant thereof at 1 MHz was measured to find that aspecific inductive capacity was 15 and that a dielectric loss tangentwas 0.008. Further, a specific gravity of the resin composite materialwas 1.24.

Example 9

The components were molten and kneaded at 270° C. by means of a meltkneading equipment in the same manner as in Example 8, except that avolume ratio of insulated ultrafine powder/PPE/PS was 20/40/40, and themixture was pelletized to obtain a resin composite material.

A dielectric constant thereof at 1 MHz was measured to find that aspecific inductive capacity was 12 and that a dielectric loss tangentwas 0.005. Further, a specific gravity of the resin composite materialwas 1.2.

Example 10

The components were molten and kneaded at 270° C. by means of a meltkneading equipment in the same manner as in Example 1, except that avolume ratio of insulated ultrafine powder/PPE/PS was 30/35/35, and themixture was pelletized to obtain a resin composite material.

A dielectric constant thereof at 1 MHz was measured to find that aspecific inductive capacity was 18 and that a dielectric loss tangentwas 0.011. Further, a specific gravity of the resin composite materialwas 1.29.

Example 11

The components were molten and kneaded at 270° C. by means of a meltkneading equipment in the same manner as in Example 8, except that theparticles synthesized in the synthesizing method 2 for insulatedultrafine powder were used, and the mixture was pelletized to obtain aresin composite material.

A dielectric constant thereof at 1 MHz was measured to find that aspecific inductive capacity was 11 and that a dielectric loss tangentwas 0.005. Further, a specific gravity of the resin composite materialwas 1.2.

Comparative Example 2

The components were molten and kneaded at 270° C. by means of a meltkneading equipment in the same manner as in Example 8, except that theparticles synthesized in the synthesizing method 3 for insulatedultrafine powder were used, and the mixture was pelletized to obtain aresin composite material.

A dielectric constant thereof at 1 MHz was measured to find that aspecific inductive capacity was 11 and that a dielectric loss tangentwas 0.04. Further, a specific gravity of the resin composite materialwas 1.2.

Example 12

The components were molten and kneaded at 270° C. by means of a meltkneading equipment in the same manner as in Example 8, except that theparticles synthesized in the synthesizing method 4 for insulatedultrafine powder were used, and the mixture was pelletized to obtain aresin composite material.

A dielectric constant thereof at 1 MHz was measured to find that aspecific inductive capacity was 10 and that a dielectric loss tangentwas 0.005. Further, a specific gravity of the resin composite materialwas 1.21.

Example 13

The insulated ultrafine powder obtained in the synthesizing method 1 forinsulated ultrafine powder and polybutylene terephthalate (PBT) weremolten and kneaded at 270° C. by means of a melt kneading equipment sothat a volume ratio of insulated ultrafine powder/PBT was 25/75, and themixture was pelletized to obtain a resin composite material.

A dielectric constant thereof at 1 MHz was measured to find that aspecific inductive capacity was 16 and that a dielectric loss tangentwas 0.01. Further, a specific gravity of the resin composite materialwas 1.45.

Example 14

The components were molten and kneaded at 270° C. by means of a meltkneading equipment in the same manner as in Example 13, except that avolume ratio of insulated ultrafine powder/PBT was changed to 20/80, andthe mixture was pelletized to obtain a resin composite material.

A dielectric constant thereof at 1 MHz was measured to find that aspecific inductive capacity was 13 and that a dielectric loss tangentwas 0.008. Further, a specific gravity of the resin composite materialwas 1.29.

Example 15

The components were molten and kneaded at 270° C. by means of a meltkneading equipment in the same manner as in Example 13, except that avolume ratio of insulated ultrafine powder/PBT was changed to 30/70, andthe mixture was pelletized to obtain a resin composite material.

A dielectric constant thereof at 1 MHz was measured to find that aspecific inductive capacity was 20 and that a dielectric loss tangentwas 0.015. Further, a specific gravity of the resin composite materialwas 1.53.

Example 16

The insulated ultrafine powder obtained in the synthesizing method 1 forinsulated ultrafine powder and polypropylene (PP) were molten andkneaded at 220° C. by means of a melt kneading equipment so that avolume ratio of insulated ultrafine powder/PP was 25/75, and the mixturewas pelletized to obtain a resin composite material.

A dielectric constant thereof at 1 MHz was measured to find that aspecific inductive capacity was 12 and that a dielectric loss tangentwas 0.008. Further, a specific gravity of the resin composite materialwas 1.07.

Example 17

The components were molten and kneaded at 220° C. by means of a meltkneading equipment in the same manner as in Example 16, except that avolume ratio of insulated ultrafine powder/PP was changed to 20/80, andthe mixture was pelletized to obtain a resin composite material.

A dielectric constant thereof at 1 MHz was measured to find that aspecific inductive capacity was 10 and that a dielectric loss tangentwas 0.007. Further, a specific gravity of the resin composite materialwas 1.05.

Example 18

The components were molten and kneaded at 220° C. by means of a meltkneading equipment in the same manner as in Example 16, except that avolume ratio of insulated ultrafine powder/PP was changed to 30/70, andthe mixture was pelletized to obtain a resin composite material.

A dielectric constant thereof at 1 MHz was measured to find that aspecific inductive capacity was 14 and that a dielectric loss tangentwas 0.009. Further, a specific gravity of the resin composite materialwas 1.12.

What claimed is:
 1. A method for producing an insulated ultrafinepowder, comprising: adding a liquid metal alkoxide to amethanol-containing organic solvent, which has a conductive ultrafinepowder comprising a carbon material dispersed therein, and furtheradding water thereto, separating a resulting solid material, and dryingthe solid material to obtain the insulated ultrafine powder.
 2. A methodfor producing an insulated ultrafine powder, comprising: adding a liquidmetal alkoxide to a methanol-containing organic solvent, which has aconductive ultrafine powder comprising a carbon material is dispersedtherein; further adding thereto a coupling agent having an alkoxidegroup; and then adding water thereto, separating a resulting solidmaterial, and drying the solid material to obtain the insulatedultrafine powder.